The development of E-UTRAN shall ensure competitiveness of future mobile communication systems in a long-term perspective, i.e. 10 years and beyond. The overall target is to further reduce operator and end-user costs and to improve service provisioning. Possible ways of reaching this target are to study ways to achieve reduced latency, to achieve higher user data rates, and improve the system capacity and coverage. One of the main novelties introduced for E-UTRAN in order to achieve these targets is the introduction of a new physical layer. This new physical layer applies Orthogonal Frequency Division Multiplexing (OFDM) for the downlink and Single Carrier Frequency Division Multiple Access (SC-FDMA) for the uplink. These choices were made, e.g., to achieve greater spectrum flexibility and enabling deployment in various spectrum allocations; to achieve the possibility of frequency domain adaptation and enabling higher spectrum efficiency; to achieve enhanced efficiency for broadcast services in the downlink due to the inherent macro-diversity combining properties of OFDM; and to achieve reduced receiver complexity, especially at high bandwidths and in conjunction with MIMO.
An evolved UTRAN can apply either a frequency-division duplex (FDD) transmission mode or a time-division duplex (TDD) transmission mode. When applying the time-division transmission mode, the evolved UTRAN uses the same frequency band for both uplink and downlink communication. Thus, some time slots are reserved for the uplink while others are reserved for the downlink. This is typically configured by the network. One time slot is assigned mandatory for the downlink, e.g. the first time slot in a radio frame. By reading control information in this time slot, the UE then knows the configuration of the other time slots, uplink or downlink.